Demonstration of nonlinear interaction of crossed turbulent streaming jets

Abstract

An experimental apparatus was built for demonstration purposes involving two mutually perpendicular crossed ultrasonic turbulent streaming jets in water. A 2D Particle Imaging Velocimeter (LaVision) measured the turbulent flow generated by their interaction. Experiments were performed in an open 10 cc acrylic water tank. The apparatus consisted of two Langevin ultrasonic transducers—both equipped with stepped horns with section diameters: 1/2, 1/4 and 1/8 in.2. A kit developed by Sonics and Materials included a 40-kHz oscillator driving a 20 W amplifier (impedance matched to the 40 kHz transducer CV245) and stepped horn (Part # 630-0594). Two such units were needed to generate the crossed ultrasonic turbulent streaming jets. In the viewing plane the axes of each streaming jet was—i cos30—j sin30, + i cos30—j sin30, respectively. The horn tips (1/8 inch) (slightly submerged in the water) also generated small cavitation bubbles. Lighthill’s theory of acoustic streaming (1978) for a single source will be discussed. Lighthill recognized the importance of “Stuart streaming,” Reichardt’s turbulent jet measurements, Schlicting’s turbulent jet theory (involving eddy viscosity) and Squire’s exact solution for a nonlinear laminar jet flow. Earlier, Lighthill predicted that a turbulent jet would generate aerodynamic sound.